As strange as it may seem, I hate my accent and want to speak like an American because I think it sounds cooler and more like how I want to sound.
I’ve more or less perfected my version of an American accent on my own, I think.
But whenever I’m with other people who know me, I revert back to my old accent instinctively because that’s how they know me to sound like. I’m unsure about how I can subtly transition without them noticing a sudden change, such as through gradual exposure to my accent changing more each time they hear it. That way I could argue that I don’t know how it happened and it was a slow progression if they eventually realise it’s different, rather than something forced that I started doing one day.
The biggest thing I think is changing the pronunciation of certain words with “a”, such as going from “fahst” to “faast” for the word ‘fast’, or “mahsk” to “maask” for ‘mask’. Because it’s really one or the other, there’s no in-between. I feel like for most other sounds, a gradual transition into more American sounds can be possible, but that one’s like, how can I make the plunge and will people notice it straight away and think it’s weird?
My sibling in Christ, just relax and be yourself. You’ll pick up the accent more and more over time, that’s how it works. Forcing it is disingenuous. Imagine if my goofy midwestern ass moved to the UK and started to try to speak with Brits forcing their accent.
I had some friends in Munich who were brothers, just two or three years apart. They both grew up learning British English, but one eventually participated in an exchange program in Canada while the other participated in one in Australia. When they came back, their English accents were completely different from each other - no matter how hard they tried to sound similar to each other. In the end, everyone though it was unique and kind of fun since one brother would sometimes use slang the other didn’t understand.
Point being, OP, is to do what feels natural. Ultimately, it’s your voice, but you’ll pick up certain things here and there that naturally change your way of speaking over time.